Audio frequency amplifier



Jan. 1, 1935.

AUDIO l H. KRAMBEER FREQUENCY AMPLIFIER led July 16, 1950 E i I I I I I4 feed-Back 1 Control 1 2 g u n -onfrol 25 Dev/be myth/77 f5 271' lINVENTOR flefecfbq KARL HE\NR\CH KRAMBEER ,2 BY)! D ATTORNEY PatentedJan. 1; 1935 invention to audio frequency amplifier adapted .to amplify.signal currents transmitted byradio; anduthe same serves the purpose tocompensate such distortion as has been occasioned in :thenr'adiofrequencyeamplifier and the rectifier by selectance driven unduly far i.e., 'byvundue selectance. I

Owing to the slight 'difierencein the frequencies, of..the carrier wavesofthe variousadjacent broadcast stations more or less perfect receptionis feasible only by :the aid of means adapted to insure greater tuningsharpness or so-called selectance. In order that two transmitter'stations may' be separated,. itis frequently necessary to push theselectance, beyond, the limit ewhere'tundistorted reception is stillfeasible The selectance of'the receiver apparatus becomes particularly.favorable if in'long-distancereception regenerative; couplingismade very.closefor the purpose ofzinsuring large volume. But distortion of bothvoice and music is then; inevitable. However, r it is chiefly the highfrequencies that arehurt, and the result is that both, voice and W musicare 1 dull-in reproduction. j p j In most instances it is impossible:to. dispense with high selectance in the tuningmeans; :Bllfiiifreception shall be made acceptable in spite of that there remains 110Other remedythau to maker-an attempt to compensate such distortion ashas been caused by undue selectance. p, p a v Now, according to thepresent invention, this compensation is insured in the audiofrequencypart of the receiver in that, by additional circuit means, or bysuitable dimensioning of-the normal transfer resistances, thedistortionsv0cmtsionecl by undueselectance are compensated, It is then possible towork with maximum selectance in the radio frequency amplifier and thisis especially important a for long-distance reception, Suchsupplementary circuit elements as are provided may be connected inparallel or in series with the plate or grid resistancesor else to theloudspeaker. It should here be noted that so far as the essential'featur'es of the basic idea of the invention are concerned itisimmaterial whether the distortion is caused'in each stage or only inonestage. When :the selectance changes and thus also the distortion, say,owing to a change in regeneration, then, according to the invention;also the distortioncompensating meansare altered; this alteration beingbrought about in a positive manner. v In the .drawingwhich showsembodiments by way of example of the idea underlying this inven 'tion: IFigure 1 illustrates diagrammaticallyone preapplied to the circuit shownin Figure 1. I

. Accordingtto Fig. 1 in series 'withthe plate re-' ferred embodimentofmy inveritionin which a resonant circuit is placed in the output-of fan7 1 amplifirtube; t t. H J t FigureZ shows the inventiondiagrammatically withtheresonant circuit placed in the input of "5anam'plifiertube'; Figure 3 illustrates anotherrembodi nentof theinvention inlwhich the resonant" circuit is placed in parallel relationto the plate and grid resist ance;.* aFigure4i1lustrates'diagranrmatically my invention'as appliedto atransformer-coupled amplifier;

and, U 7 Figure 5 illustrates diagrammaticallya way-of obtaining'variable distortion comp'ensation' as 5 sistance',;there isico'nnectedastopper circuit comprising? condenseriC and coillLin parallel, in aresistance-coupledgaudio' frequency amplifier. 'If the circuit elements-are suitably proportioned, aniplification.i..for. the frequency 'rangein [the neighborhood of resonance of the-stopper circuitmay-.bel.lpromoted. Choosing a"resonanceifre'-' quency 5ofarou1'id"f="8000; this makes it feasible to insure compensation of thedistortion caused b'y undue-radio frequency selectance'H-In said cFigure 1 a first tube 1 preferably coupled to a source of energy to beamplified by'means of impedance 23is provided with an output circuitcomprisingan impedance element 3, an inductance L'shuntedby' a condenserC and the 'usualsource of anode current; The anode of the tube 1 isconnected to the grid element of a-second tube 2 through. couplingcapacity l. impedance e1e ment 5 is connected-between the gridandcathode of the tube 2. Terminals; 6 and 7 representthe output terminalsof thedevice to which may be connected anysuitabletypeoftranslatingde'vice. From what has preceded it is obvious that theoutput'of'the tube lfis impressed upon the input oftube2. 4 I 1 jThesame result is realized'if astopper circuitis connected hrseries withthe grid leak as shown in Fig. 2. In Figure 2 the output circuit of tube1 is provided with an impedance 22. As shown,- the anode of tuber-lisgconne'ct'edrto the 'grid of'tube 2 throughfi; coupling capacity? 4and tube 2 11s provided with a gridtleak 21 series .With thestopper'circuitim; in-thecase of Figure: 1 termi '6 nals 6 and"? of'Figure'2 are the outputf tenninals resistancearesonantcircuit(condenser and coilin series) is disposed which is tuned to a lowfrequency (Fig. 3). In Figure 3 two tubes 1 and 2 are shown cascadedthrough a coupling condenser 4.

.Tube 1 has connected between the anode and any suitable translatingdevice may be connected."

The invention is useful also combination with transformer-coupled audiofrequency amplifiers. As shown in Fig. 4 the desired compensation ofdistortion may here be accomplished by shunt ing the primary or thesecondary'winding of the transformer by a condenser 20. In Figure '4 thetubes 1 and 2 are transformercoupled; purpose transformer T is providedwith a 'p'ri rmary 17 which is associated with the output of tube 1 anda secondary 18 shunted by a; condenser 20, connected, between the; grid1 and cathode. .of

tube2.,j

In the presence of suitable dimensions the selfcapacity of thetransformer representedby condenser 19 shown in dotted lines may beutilized for this purpose so that additional circuit-ele-v ments forthatpurpose are dispensable.

As already pointedout radio frequency selectance and the distortioncaused thereby depends markedly upon the feed-back setting of theaudiontube. The reception of long-distancestations, when. theregenerativecoupling is very close, is attended by far more distortionthan is trueof local broadcasters- But if perfect reception shall beinsured in all cases, then the antidistortion means hereinbeforedisclosed/must be adjustableor regulable in sucha way that the degree'ofdistortion compensation must always be closely adapted to the feed-back.These simultae neoussettings may also be joined or made interdependent;in a positively, acting manner.

. Variable distortion compensation. may. be in-.- sured, for instance,in a circuit scheme of the kind illustrated in Fig. 1 by that avariable. high-ohm resistance is 'connectedin. parallel relationship; tothe stopper circuit (Fig.5) g

1 'In Figurefi tubes land 2 are coupledthrough the sametypeof circuit asshown in Figurel. However, in this case there is provided a variabletone control device 8. The input of the tubev 1 is connected to theoutput of. -a tunable radio .frequencyjamplifier and detectorcircuit. 10as'shown. The device-.10 is provided with a feedback control 13connected to 10 through conductors 24 and 25. Device 13 is'shownvariable and is adapted to be uni-controlled through a common shaft orother suitable interconnectingmeans 14 with the tone control; 8.Numerals 11 andu12 represent generally the antenna and ground of theusual radio receiver. i 7 Whereaudio frequency amplifiers havinga-plurality of stages are employed the means hereinbefore disclosed maybe inserted. either above or resulting in :giving the selector circuitsuch sharp selectance characteristics that signal Qenergypassed-,therethrough is distorted in various degreesdepending upon theadjustment of the se-& lectivity contrOLa detector and. an audi freequency amplifier, said audio frequency amplifier being provided with aresonant circuit the resonance characteristics of which tend tocompensate for the radio frequency circuit signal distortion and meansfor varying the compensating characteristics of said resonance circuitsimultaneously with thevariations adjustment of the selector circuit forthe different degrees of selectivity whereby the signal distortioncompensating "means varies simultaneously with the variations intheselectance characteristics of the selector circuit to therebycompensate for the various degrees of distortion.

2. Ina radio signalling system, a radio frequency circuit, adjustablemeans associated with 'said'circuit the operation of which affects theselectivity characteristics of said circuit, an audio frequencyamplifier, means for controlling the -.tone o f -said amplifier andadditional means for rendering said tone control means simultaneouslyoperative with said adjustable means whereby the-tone control meanscompensates for any signal distortion caused. by adjustments in the saidadjustable means. ..3. in asigna'lling systemincluding a:tunab1eselector circuit anda signal amplifier, an adjustable selectivitycontrol means associated with the selector circuit, an adjustabledistortion compensating means associated with the signal'amplifier andasingle means for adjusting both said last namedmeans simultaneously. 4.In .a radio :receiver, a tunable radio frequency circuit, adjustablemeans associated with said circuit, operation of said. adjustable meansacting to affect the selectivity characteristic of saidcircuit, adetector, an audio frequency amplifier,. means for controlling the toneof said amplifier and additional means for rendering said tone controlmeanssimultaneously operative with said adjustable. means.

'5..Themethod of maintaining substantially uniform tone-fidelity inradio receivers and the like providedwith radio frequency and audiofrequency amplifiers of the type wherein acharacteris'tic of theiradiofrequency amplifier is controllable between two extreme conditions andwherein variations in said characteristic causes inherent variations inthe selectivity characteristic of the amplifier which comprisessimultaneously varying the ratio of high-to-low frequency response ofthe audio frequency amplifier with variations of the selectivitycharacteristic ofthe radio frequency amplifier.

6. In radio signalling apparatus, a radio frequency selector circuitprovided with adjustable means operation of-which 'varies at least twocharacteristics of said circuit one of which is theselectivityof thecircuit, an audio frequency circuit,- adjustable means for controllingthe tonal characteristics of said audio frequency bin cuit and singlemeans for renderin'g'the tone control simultaneously operative "withsaid first named adjustable means said tone control means acting tocompensate for any signal distortion caused by adjustments in the firstnamed means.

'7. In a radio receiver, a radio. frequency circuit, adjustable meansassociated with saidcircuit operation thereof acting to vary a characteristic of said circuit, variations of said characteristic of saidcircuit also acting to vary the selectivity characteristic of said radiofrequency circuit an audio frequency amplifier, means for controllingthe tonal characteristics of saidampli-fier and means for rendering. thetOIIE'COI-IUIOI means simultaneously operative with said adjustablemeans whereby the tone control means compensates for anysignaldistortion caused by changes'in the selectivity characteristics of saidradio-frequency circuit.

8. A radio signalling system comprising in combination a radio frequencyamplifien, an audio frequency amplifier, adjustable means associatedwith said radio frequency amplifier and operable by a control memberacting upon operation to vary at least two different characteristics ofthe radio frequency amplifier, one i,

of said characteristics beingthe selectivity thereof, and means operableby said control member for varying the ratio of high-to-low frequencyresponse of said audio frequency amplifier simultaneously withvariations in the selectivity of the radio frequency amplifier tothereby compensate for any sign l distortion caused by vaamplifier. a 7

' KARL HEINRICH KRAMBEER.

riations in the selectivity of the radio frequency a 1

